1. Field of the Invention
The present invention relates to a structure of a hydraulic circuit for an automatic transmission and more particularly to a hydraulic circuit for an automatic transmission in which a communicating passage formed in a control valve body communicates between fluid passages provided in a transmission case.
2. Prior Art
Generally, as disclosed in Japanese Patent Application Laid-open No. Toku-Kai-Hei 8-177890, a hydraulic circuit of a continuously variable transmission is formed such that a hydraulic pressure generated by an oil pump provided in a transmission case is supplied to hydraulic actuating chambers such as a primary pulley actuating chamber, a secondary pulley actuating chamber and the like through fluid passages provided in the transmission case.
In most cases, the transmission case is divided into a main case and a subsidiary case for the sake of assembly convenience. Therefore, in this case, in order to communicate between the main case and the subsidiary case with a fluid passage, a dedicated conduit such as a lubrication pipe must be installed therebetween.
However, it is not so easy to provide such a dedicated pipe in a narrow transmission case. Further, since the location suitable for connecting the pipe to the transmission case is limited, the configuration of fluid passages formed in the transmission case becomes complicated. Such complicated fluid passages are difficult to be cast. Further, it is not realistic to make such complicated fluid passages by machining.
Furthermore, the forgoing lubrication pipe needs an additional man-hour for installation and the number of components increases.